In the field of application of exterior coatings to architectural structures, wheeled vehicles, ships, aircrafts, etc., there are utilized high-quality polyester or acryl type exterior coatings since the coatings used for the purpose intended are required to have excellent weathering resistance and permanence properties. However, outdoor durable years of existing coatings are short and even the above-mentioned high-quality coatings will lose their fine appearance and substrate protective properties in several years.
Because of their being excellent in weathering resistance, water resistance, solvent resistance, chemical resistance, release properties, low friction characteristics and water repellency, fluorine-containing polymers which are also quite stable thermally and chemically are suitable for use as surface treatment agents for various kinds of substrates or base materials. However, on account of their excellent properties as mentioned above, conventionally known fluorine-containing polymers are difficult to use as coating materials because they are difficultly soluble in organic solvents and hard to form films thereof. For instance, most of coating materials of fluorine-containing polymers known at present are powder coatings except for PVdF (polyvinylidene fluoride) which is used as an organic solvent dispersible type coating by utilizing its properties of being soluble in specific solvents at elevated temperatures. Moreover, since coating materials of fluorine-containing polymers mentioned above require high temperature baking at the time when their films are formed, the field in which they are used is limited to such places where heating equipments can be arranged. Furthermore, such heating equipments and baking step as required for the utilization of these coating materials are undesirable from the standpoint of the safety of workers engaged in the coating operation or the work environment. Under the circumstances, various attempts have been made in recent years to develop fluorine-containing polymers which are soluble in solvents or which do not require a high temperature baking step.
For example, Japanese Patent Laid-open Publn. No. 34107/1982 discloses quaternary copolymers comprising fluorolefin, cyclohexyl vinyl ether, alkyl vinyl ether and hydroxyalkyl vinyl ether, said copolymers being alleged to be soluble in organic solvents and capable of curing at ordinary temperature. However, for curing these copolymers at ordinary temperature, it is necessary to use melamine type hardeners or urea resin type hardeners, and hence the mode of using these copolymers is of the two-liquid type, resulting in reduced working efficiency. Furthermore, the glass transition temperatures of these copolymers are relatively high such as above ordinary temperature, i.e. 25.degree. C. Moreover, Japanese Patent Publn. No. 39472/1971 suggests, though no concrete example is shown, that polymers obtained by mechanically treating PTFE (polytetrafluoroethylene) with organosilicon compounds having olefinically unsaturated bonds and hydrolyzable groups in the presence of such radical initiators as organic hydroperoxide are crosslinked and cured with water at ordinary temperature. The polymers prepared according to the above process, however, are polymers in which the organosilicon compounds have grafted on PTFE and are substantially insoluble in organic solvents.
Under the present circumstances, no fluorine-containing polymers which are soluble in organic solvents and curable at ordinary temperature are available.